The present invention is directed to a method for automatic assembly and testing components on a printed circuit board to form an electronic card module in which the assembly is accomplished by a program-controlled assembly and testing automats on which the card modules are supplied in the course of the production flow by a mechanical conveyor system.
Reducing inventories and avoiding technically and dispositively caused reassembly or, respectively, rejects, are significant contributions for boosting productivity. This is especially true of the production of electronic systems that are manufactured from a combination of high-grade components. Card module production and testing is the focal point of such operations.
Inventory costs are caused by the number of modules produced during a run, which numbers depend on the run time and by the inventory of the completely tested card modules which cannot yet be called in by a following systems assembly because the type structure is not yet complete. Reassembly and reject costs are caused by card modules, which are no longer required after manufacture due to a modified disposition or, respectively, due to the modules becoming technically obsolete by the time they are needed. The risk is directly related to the overall number of modules produced during each run.
It is known to produce module cards in lots wherein the reason for establishing these lots lies in that the assembly and testing machines must be specifically equipped for the production of a specific type of card module. Supplying the machine with material such as components as well as with the information sets that are defined in the operational sequences are included in the equipping process. Because the setup time is currently relatively high in comparison to the actual manufacturing process, an attempt must be made to produce the greatest number of identical card module types in succession after the exertion of the setup time which establishes the lots. Known card module production devices produce the required spectrum of card module types in large quantities in a cycle of, for example, a number of weeks and supply them to a card module storage from which the following assembly shop can optionally take the card modules. This module storage or buffer storage is necessary in order to keep adequate piece numbers of a specific type of card module on hand because the same type will not be produced again until after a given time span of several weeks has passed.
The lots combine the need of the period of the system assembly, for example, a monthly number. The production and testing facilities must be re-equipped for every lot. One lot is not forwarded to the following production step until the last unit has been processed. The combination of the card modules of the same type is an absolute necessity in order to keep the setup times in a justifiable ratio to the production times. All known activities are concerned with the gradual improvement of the present situation without departing from the fundamental prerequisite of establishing lots. A running, which is time on the order of, for example, two weeks for production of a given type of card module which includes calling in material up to the conclusion of the electrical testing, seems to be a natural lower limit. This value, however, can only be achieved when the lot size is reduced to a limit at which the setup outlay no longer becomes economically justifiable because with a lot size of 15 to 20 items, the setup costs have an exponential increase.